Climate change's effect on extreme weather

Kerry Emanuel: Well I'm trying to get folks to understand that climate change doesn't just affect the mean temperature and rainfall, but also affects extreme events. In fact, what we're seeing with hurricanes is a shift toward higher intensity events, more Category 3 through 5 type storms and a big shift toward much heavier rainfall as we have seen in Harvey. We can't say much about individual storms like Harvey and Irma, but we can say quite a bit about how the underlying probabilities of events like those are changing.

Frank Graff: Is that because of warmer seas? Warmer air that can hold more moisture? All of the above?

Kerry Emanuel: Hurricanes are powered by the evaporation of sea water. So, what we're concerned about is what we call the potential evaporation—what's the maximum rate of evaporation you can have—and that goes up as the climate warms. It's not just the ocean temperature or the atmospheric temperatures. It’s a combination of those.

But it's easily calculated and when we calculate that, it has been going up. And the climate models project that it will continue to go up. So that's the main source of concern.

The other piece of physics, which is very straightforward and everybody actually knows, we're sitting here on a warm night and it's humid—when you have greater warmth, you have more humidity and that translates to more rain from hurricanes.

Frank Graff: So when you look back a few years and 2017… What we've seen this year is going to be more the norm?

Kerry Emanuel: Yeah, I think the way we would put it is that an event that had a certain probability, say, 30 years ago has a higher probability today. It will have a higher probability, say, at the end of the century. So, the underlying probabilities are shifting and rather dramatically. In 1990, we estimated for the state of Texas that Harvey’s rainfall was about a one in 100 years event. That’s an annual probability of one percent. We think by the end of this century it will be a 20 percent annual probability, or one in five or six years. And it's already 2017. It's probably already something closer to a two or three percent probability.

Coping with climate change

Frank Graff: What do you say to people, and I'm sure you've heard them say, "The weather is going to change, this was kind of a fluke." What do you say?

Kerry Emanuel: As a species we're hardwired to detect short changes in our lifetime and changes in the weather and so forth. And detecting underlying climate change is really not in our gene pool. So, you have to have faith in observations and be able to look at them over a hundred years and not just one year.

You have to be astute enough to detect the signal in the noise. I mean I like to say, I can't forecast the weather 10 days from now, but it doesn't mean I can't say that summer is warmer than winter. I'm not saying that July 1st will necessarily be hotter than January 1st, but very probably so.

And if you try to detect on the other hand how the climate warms during the spring, you can go for a whole month (as most people know who live in the northeast or I suspect even down here) and not find a tendency in the temperature.

But we all know that summer will eventually arrive. One has to put one's faith in science and that's difficult for some people to do.

Frank Graff: Are we at a point where we really can't prevent climate change, that we can maybe change enough to mitigate, but we've got to adapt to it now? This is the reality, we've got to get ready going forward?

Kerry Emanuel: Well I would say we can prevent a lot of climate change still. We've already had some climate change and so that's water over the dam. So, we have to do both. We have to try very hard to prevent it because it will save us a great deal of money in the long run, and save our children and our grandchildren money.

And we're going to be forced to adapt to it as well. So, my message to the U.S. population is that the rest of the world is demonstrably transforming away from carbon-based energy sources. Whether you agree with it or like it, it's happening and it's a huge market opportunity.

It’s not just the risk it's an opportunity. And China is seizing that. They're building all the solar panels, they're way ahead in wind turbines, ahead in new vision nuclear power, and we're going backwards to coal.

The energy market is a six trillion-dollar annual market, which is a third of U.S. GDP. And we're giving it up. And even if you don't care about climate change you should care about that. Because we still have an edge in innovation. We should be leading the charge toward the transformation of our energy economy.